An antibody or antigen that reacts with cells or substances from different species; used in biology and immunology.
From Greek hetero- (different) + -phil (lover of). This medical term was coined in early 20th-century immunology to describe antibodies that cross-react with antigens from different organisms.
Heterophils are antibodies that are like cross-species communicators—they can recognize antigens from different animals! This is actually how the old 'rabbit test' for pregnancy worked, using heterophil antibodies to detect human pregnancy hormones.
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